For the operation of two-stage compressors, with at least one cylinder and piston unit for preliminary compression and with a second cylinder and piston unit of smaller capacity for the second stage of compression, and similar machines, relatively very large peaks of torque occur during the cycle, making it necessary to have a high installed power (particularly with an electric motor) to ensure the regular operation of the machine. At the present time, use has been made of compressors having a large number of cylinder and piston systems to limit the peaks of torque (and of power), which entails high costs and large overall dimensions, as well as limited efficiency and difficult maintenance.
The object of the invention is to provide a simple machine, with a limited number of cylinder and piston systems operating in series (in practice, only two cylinder and piston systems operating in series), with the consequent advantages.
These and other objects and advantages will be made clear by the following text.
To achieve the objects indicated above, the invention relates to a machine such as a compressor of the two-stage type, with a pair of cylinder and piston systems operating in series and driven by a crankshaft, in which the two pistons are driven with a minimum phase difference, to reduce the peaks of torque.
Preferably, the two pistons are driven with a zero phase difference, so that the crankshaft can rotate equally well in one direction or in the opposite direction.
The invention also relates to a crankshaft for compressors and other equivalent machines, in which two cranks are positioned with a minimum or even a zero phase difference. Said shaft is to be appropriately balanced by the use of suitable counterweights.